The present invention relates to a copper fin material for heat-exchanger suitable for the heat-exchanger to be used under the severe conditions of corrosive environment of cars etc. and a method producing the same. It has made it possible in particular, to improve the corrosion resistance and to thin the fin without decreasing the thermal conductivity as a fin.
Recently, a trend in thinning the fin material for heat-exchanger has been accompanied by the lightening in weight of heat-exchanger for cars. While, on the otherhand, the corrosion due to the salt damage caused by snow-melting material etc. has become a problem The severe corrosion of fin material due to salt damage is affecting seriously on the heat-exchanger in such ways as the decrease in the radiating characteristics, the deterioration in the strength and the like.
In general, improvements in the strength, corrosion resistance, etc. are all desired for the fin material for heat-exchanger. With respect to the improvement in the corrosion resistance, the improvement is possible even by alloying the material itself through the addition of second and third elements as, for example, Cu-Ni type anticorrosive alloy. This brings about, however, not only an increase in cost resulting in the economical disadvantage, but also a drastic decrease in thermal conductivity (electroconductivity). Hence, even if the fin material may be excellent in the aspect of corrosion resistance, it ends up to become quite unsuitable as a fin material for heat-exchanger, high electroconductivity being desired therefor.
On the otherhand, the corrosion is originally a phenomenon on the surface. Thus, if deciding to modify only the surface of material, it should also be possible to suppress the decrease in the electroconductivity to a low degree and yet to improve the corrosion resistance. Based on this thought, a fin material for heat-exchanger having a diffused layer of Zn formed on the surface of highly electroconductive copper-based material, protecting the inside core material by a mode of sacrificial anode, and retaining the electroconductivity by the core material has been proposed, for example, as a fin material for car radiator. In fact, a distinct effect on the improvement in the corrosion resistance can be seen by forming the diffused layer of Zn on the surface, but, the diffused layer of Zn formed on the surface layer is restricted to several .mu.m or so per side in thickness and that, in this case, the surface becomes a Cu-Zn alloy, so-called brass, there is a problem that the Zn disappears through the dezincificative corrosion inherent to brass, and thus, the sacrificial anode effect of Zn cannot be retained over a long term.
As described above, although the diffused layer of Zn formed on the surface layer is restricted to several .mu.m or so per side in thickness, if the dezincificative corrosion inherent to brass can be suppressed and prevented effectively, the fin material for heat-exchanger more excellent in the corrosion resistance could be expected and the thinning would also become possible.
In order to suppress such dezincificative corrosion inherent to brass, a method is conceivable wherein third element effective on the improvement in the corrosion resistance is added into the diffused layer of Cu-Zn for making the Zn-diffused layer itself highly corrosion-resistant.
Various elements can be considered for suppressing the dezincificative corrosion. However, the decrease in the thermal conductivity when adding these elements to copper ends up generally becoming large compared with that when adding same amount of Zn. Hence, if these elements are added to the entire diffused layer in a sufficient amount to suppress and prevent effectively the dezincificative corrosion etc., the corrosion resistance would be improved, but the decrease in the thermal conductivity would end up becoming large.
As a result of extensive investigations in view of this situation, a copper fin material for heat-exchanger excellent in the corrosion resistance and the thermal conductivity and a method of producing the same have been developed according to the invention, wherein the dezincificative corrosion of Zn-diffused layer formed on the surface of Cu or Cu alloy strip is alleviated and the decrease in the thermal conductivity arising from the addition of third element into Zn-diffused layer is lessened.